A paper sheet processing apparatus such as a postal item processing apparatus which handles postcards, letters, and the like includes, e.g., a pickup device, a determination device (OCR), a stacking device, a reject (RJ) stacking device, a switchback device, a conveyance path which connects the respective devices, and a gate which distributes conveyed paper sheets (postal items) to the respective devices. A plurality of paper sheets set at the supply portion of the pickup device are separated and picked up one by one by the pickup device, and fed to the determination device. The determination device determines the paper sheet, and decides the destination of the paper sheet, e.g., the RJ stacking device or the stacking device. After that, the paper sheet is conveyed to the chosen device via the conveyance path and gate mechanism, and undergoes various processes inside the device.
As the pickup device of the paper sheet processing apparatus, there has been provided a suction pickup device which sucks a paper sheet by a negative pressure and picks it up. This pickup device has an air suction structure which sucks a paper sheet by using a perforated belt, air chamber, and valve device. The pickup device can pick up, one by one, paper sheets fed from the supply portion by ON/OFF-controlling suction by the valve device for each paper sheet.
In the paper sheet pickup device using this air suction structure, suction and separation of a paper sheet with respect to the suction belt are performed by switching the inside of the air chamber installed on the rear surface of the suction belt between a negative pressure and a positive pressure. The pressure in the air chamber is switched by opening and closing the valve. In a conventional method, the air chamber and valve are installed at distant locations, and a pipe connecting the air chamber and valve is relatively long. For this reason, no negative pressure is generated in the air chamber until the air in the pipe is drawn, or the inside of the air chamber does not return to a positive pressure unless air is supplied into the pipe. Even if the valve itself operates quickly, time is taken to switch the inside of the air chamber between a positive pressure and a negative pressure. In addition, the inertia of a disk itself constituting the valve is large, which is disadvantageous for high-speed rotation and stopping. It is therefore difficult to suck and separate a paper sheet at a higher speed and stably pick it up at a higher speed.